リファレンス
Tied hands: synchronism between beak development and feeding-related morphological changes in ommastrephid squid paralarvae.
Franco-Santos, R. M., & Vidal, E. A. G. (2020). Hydrobiologia, 847(8), 1943-1960.
https://link.springer.com/article/10.1007/s10750-020-04223-z
要旨
Ommastrephid squid produce some of the smallest cephalopod hatchlings, whose feeding behavior has not been observed. The present study aimed at indirectly filling this knowledge gap by describing ontogenetic changes in beak morphology and morphometry and integrating these results with published datasets on Illex argentinus arm crown morphology and gut contents. Individuals [0.7–15 mm mantle length (ML)] were measured, weighed, and had their buccal mass extracted. Jaw measurements were correlated with ML to determine whether jaw development occurred linearly with ML. For a 10 mm increment in ML, weight increased 430-fold. The jaws of hatchlings were rudimentary, but in larger paralarvae the rostrum protrudes and the jaw features (teeth, slit, groove) disappear. Increases in ML were predicted by beak robustness indices and rostrum protrusion, with growth discontinuities pointing to faster growth in individuals ≤ 2 mm ML. Morphological changes in the beak and arm crown are in synchrony with a transitional event in the feeding ecology of paralarvae: the onset of active predation on crustaceans and masticating their exoskeletons for ingestion. Integration of the results with published data has led to the proposal of a hypothesis of four size-differentiated developmental stages in the feeding ecology of I. argentinus rhynchoteuthions.
コメント
アカイカ科のイカ Illex argentinus の孵化稚仔 (rhynchoteuthion幼生) について，口器である嘴 (beak，いわゆるカラストンビ) の形態の成長に伴う変化を調べた論文．さらに腕の形態変化の知見とも合わせて，幼生期の食性の変化と形態変化の関係性を考察している．アカイカ科のイカは他のイカのように孵化直後から成体とおなじように餌を捕るのではなく，特殊な幼生の段階を持つがその生態の理解はなかなか進んでいないため，このような知見は食性の理解のためにもとても重要． ただ，個人的には他の一般的なイカにおける嘴の発生過程も気になるところ．イカの年齢推定のために嘴自体の形成過程を調べた論文は多いが，口器全体の構造がどのように形成されているのかということを調べた研究はあまり見当たらない．この研究ではSEMの画像なども有効に利用しているので，意外とそのような手軽なアプローチでも新しい知見が得られるのかもしれず，興味深いところ．
